1. Field of the Invention
This invention relates to ultrasonic measurement, and is of particular use in measuring inaccessible surfaces, for example measuring the cylinder wall thickness in water cooled internal combustion engines.
2. Description of the Prior Art
Cylinder blocks, i.e., for internal combustion engines, are usually cast, as from iron, using mold cores to define the cylinder bores within an engine block. The blocks are subsequently machined on automatic apparatus, this including machining of the cylinder bores to a suitable finish for the pistons. In a known arrangement, reference surfaces are machined on the block after casting to provide a datum position for the subsequent automatic machining. These reference surfaces are positioned by reference to a predetermined point on the casting and, owing to minor errors in the placement or movement of the cylinder mold cores prior to completion of casting; may not give an exact reference for machining the cylinder bores which may therefore be machined eccentrically in relation to the center of the mold core. In extreme cases the cylinder bores may have a non-machined strip, or may be over machined at one side giving a dangerously thin portion of cylinder wall.
One object of the present invention is to provide an improved method of and apparatus for examining articles such as cylinder block castings. A more general object is to provide an improved form of ultrasonic testing.